1. Field of the Invention
The present invention relates to a technology for conveying waste toner scraped from a surface of a target surface to be cleaned to a waste-toner collecting container in an image forming apparatus.
2. Description of the Related Art
An electrophotographic method has been widely used in an image forming apparatus such as a printer, which is connected to a personal computer, etc., and a facsimile. In recent years, a digital recording technology is applied not only to the printer but also to a typical copier, and a progress has been made in development of a digital copier. Therefore, a demand for the digital copier is expected to increase more and more. Such a digital copier is desired to have a compact size and to form high quality images at high speed considering an enhancement of efficiency in an office environment. Furthermore, the digital copier is desired to have a long lifetime for reducing a burden on the environment. Meanwhile, colorization of the image forming apparatus has been progressing, such as a color copier and a color printer.
A color electrophotographic apparatus of a revolver type or a tandem type is widely used. The revolver-type electrophotographic apparatus includes a plurality of developing units for a plurality of different colors around a single photosensitive element, and form a color image by forming a color toner image on the photosensitive element and transferring the toner image onto a recording medium such as a print sheet. The tandem-type electrophotographic apparatus includes developing units for respective photosensitive elements arranged in line, and forms a color image by forming a toner image of a different color on each of the photosensitive elements and sequentially transferring toner images on a recording medium in a superimposed manner.
The revolver-type electrophotographic apparatus includes only one photosensitive element, so that a relatively compact apparatus can be achieved. However, the toner images need to be formed on the photosensitive element in order in a plurality of stages, so that the revolver type is disadvantageous in high-speed image formation. On the other hand, although the size of the tandem-type electrophotographic apparatus is relatively larger, it is advantageous in high-speed image formation. Because the color image forming apparatus is desired to form an image at a speed similar to the speed of a monochromatic image forming apparatus, the tandem-type image forming apparatus is attracting more attention. A photosensitive element having a smaller diameter is often used to reduce the size of the image forming apparatus, which however constrains the layout of the apparatus, i.e., other units such as charging units, developing units, cleaning units, and an intermediate transfer device also need to be reduced in size. Therefore, the image forming apparatus is required to function effectively regardless of the size thereof.
The tandem-type image forming apparatus is shown in FIG. 7 as an example. In the tandem-type image forming apparatus, toner images of black (Bk), cyan (C), magenta (M), and yellow (Y) are sequentially transferred onto an intermediate transfer belt. Because an operation of forming a toner image is virtually the same for each color, the operation for forming the black toner image is explained as a representative. The tandem-type image forming apparatus includes an image carrier 1 (including four image carriers for four colors of Bk, C, M, and Y), a charging unit 2 (including four charging units for Bk, C, M, and Y), a developing unit 4 (including four developing units for Bk, C, M, and Y) in which a developer 5 is contained, an intermediate transfer belt 6, a transfer roller 7 (including four transfer rollers for Bk, C, M, and Y) arranged across the intermediate transfer belt 6, a secondary transfer unit 8, and a fixing unit 9. The charging unit 2 uniformly charges a surface of the image carrier 1. An exposure optical system emits a laser beam 3 to expose the surface of the image carrier 1, thus forming an electrostatic latent image on the image carrier 1. The developer 5 in the developing unit 4 is conveyed onto the surface of the image carrier 1 to develop the latent image into a visible image (toner image). The toner image on the surface of the image carrier 1 is transferred onto a surface of the intermediate transfer belt 6 at a nip portion at which the transfer roller 7 is in pressure contact with the image carrier 1 with the intermediate transfer belt 6 sandwiched therebetween. In the similar manner, a cyan toner image, a magenta toner image, and a yellow toner image are transferred onto the surface of the intermediate transfer belt 6 in a superimposed manner, so that a color toner image is formed on the surface of the intermediate transfer belt 6. The color toner image is transferred onto a recording medium at the secondary transfer unit 8. Then, the recording medium with the color toner image transferred thereon is conveyed to the fixing unit 9 at which the color toner image is fixed to the recording medium. The developer 5 remaining on the surface of the image carrier 1 after the transfer is removed by a cleaning blade 11 arranged in a cleaning device 10 for the subsequent image formation. Waste toner that is scraped by the cleaning blade 11 is conveyed and stored in a waste-toner storage container (not shown).
In the image forming apparatus, for reducing a cost, a one-component toner, which is relatively not expensive, is often used as material for the developer. The one-component toner has low melting point for forming a high-quality image at high speed and is applied with an external additive such as silica for enhancing handling capability. When using the toner, if toner particles get accumulated in a waste-toner conveying path, the toner particles may adhere to each other and become agglomerated, so that, a so-called blocking may occur. Especially, in the waste-toner conveying path, because deteriorated toner particles get accumulated, the toner particles are highly likely to become agglomerated, thus causing the blocking. This results in failure in operation of the image forming apparatus, which may lead to a breakdown of the apparatus.
For enhancing conveyability of the waste toner, a waste-toner conveying device is generally configured such that a waste-toner collecting container is arranged at a lower side of the waste-toner conveying path and the waste toner is collected by gravity or an external force is applied for collecting the waste toner. However, in the recent image forming apparatuses, such as a copier, a printer, etc., that use the electrophotographic method, for ensuring a high image quality, colorization, and downsizing of the apparatus, the internal configuration of the image forming apparatus is becoming more complex. Due to this, arranging the waste-toner collecting container in the lower portion of the waste-toner conveying path for the waste toner after cleaning is becoming difficult.
Therefore, a conveying unit for conveying the waste toner that is scraped during the cleaning to a collecting unit needs to be arranged at a different position.
Especially, toner particles become agglomerated more not only because of the use of the toner having the characteristics mentioned earlier but also because of the physical deterioration of the toner by repeatedly performing image formation and the thermal degradation of properties of the toner due to a temperature rise inside the image forming apparatus by heat transmission mainly from the fixing unit. Due to this, the toner may accumulate inside the conveying path, which causes clogging of the toner in the conveying path. To overcome the drawbacks mentioned earlier, various technologies have been proposed.
In a technology disclosed in Japanese Patent Application Laid-open No. 2005-43415, a cleaning hole is formed in the conveying path for cleaning the inside of the conveying path. In a technology disclosed in Japanese Patent Application Laid-open No. H11-327397, a scraping unit is arranged on a screw inside the conveying path to improve efficiency in conveying the toner, thus preventing clogging of the toner.
However, in the technology disclosed in Japanese Patent Application Laid-open No. 2005-43415, a user needs to frequently clean the inside of the conveying path. Moreover, the toner scatters while cleaning, which is problematic for environmental safety. In the technology disclosed in Japanese Patent Application Laid-open No. H11-327397, because the scraping unit is additionally needed, the number of components increases and abnormal noise may occur due to imparting of shock caused by the scrapping action.